NES expansion port pinout

Pinout of 48-pin NES expansion port

                                     +-------\
                                 +5V |01   48| +5V
                                 Gnd |02   47| Gnd
                            Audio in |03   46| NC
                                /NMI |04   45| out 2 ($4016 write data, bit 2)
                                 A15 |05   44| out 1 ($4016 write data, bit 1)
                                EXP9 |06   43| out 0 ($4016 write data, bit 0, strobe on sticks)
                                EXP8 |07   42| EXP0
                                EXP7 |08   41| EXP1
                                EXP6 |09   40| EXP2
                                EXP5 |10   39| EXP3
($4017 read strobe) /OE for joypad 2 |11   38| EXP4
                         joypad 1 D1 |12   37| /OE for joypad 1 ($4016 read strobe)
                         joypad 1 D3 |13   36| joypad 1 D4 (before inverting buffer)
                                /IRQ |14   35| joypad 1 D0 (likewise)
                         joypad 2 D2 |15   34| duplicate of pin 37
                         joypad 2 D3 |16   33| joypad 1 D2
                 duplicate of pin 11 |17   32| CPU D0
                         joypad 2 D4 |18   31| CPU D1
                         joypad 2 D0 |19   30| CPU D2
                         joypad 2 D1 |20   29| CPU D3
                           Audio out |21   28| CPU D4
                           Video out |22   27| CPU D5
       unregulated power adapter vdd |23   26| CPU D6
                     4.00MHz CIC CLK |24   25| CPU D7
                                     +-------/